Shufflebrain

The cerebral cortex is far from the only dimensional processor in the brains of organisms (although it may very well be the most elegant one in there). The frog, for instances, has a well developed roof on its midbrain--the tectum I mentioned in chapter 3: the part that helps process visual information among non-mammalian vertebrates. While the tectum comes nowhere close to the capabilities of a primate visual cortex, it nevertheless integrates different dimensions of the frog's visual perception.[14]

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Another structure I mentioned in chapter 3 was the zucchini-shaped hippocampus, lesions of which induce short-term memory defects and make it difficult for persons so afflicted to repeat newly presented phrases or sequences of numbers. In rats, however, the hippocampus appears to assist navigation.

The function of the rat's hippocampus became evident in studies involving what is called the radial maze.[15] This kind of apparatus consists of typically a dozen alleys leading off a central choice point like the spokes radiating from the hub of a wagon wheel. To win a reward, the rat must go through the alleys in a predetermined sequence. To carry out the task, the rat must remember which alley he's in and which turn to take for the next one. The rat must compile at least two sets of memories: one of positions, the other of direction. Lesions in the hippocampus erode the animal's efficiency at the radial maze.

Now think of what happens when we recite the lines of a poem. We must remember not only the individual words but, so as to place correct emphases, their location in the sequence.[16] Although the task assumes verbal form in a human being, its informational aspects seem quite like those a rat uses to organize memories of geographic locations and sequences.

At the same time, clinical and laboratory evidence don't prove that the hippocampus is the exclusive seat of such short-term memory processing. Lesions do not totally nullify the rat's ability to run the radial maze: performances dropped from 7 correct turns out of 8 to 5 or 6, a statistically significant drop but far from the total loss of the ability that follow from destruction of the seat of the neural information. [17] I once watched a record film of a man with a damaged hippocampus. He made errors when repeating phrases, but he wasn't always wrong. In addition, he often employed subtle tricks to recall items. When he was allowed to count on his fingers, he could often correctly repeat phrases that he couldn't handle without them. Other parts of the brain can compile memories of position and distance but would seem to do with much less efficiency than the hippocampus.

The success or failure of a particular behavior may depend on how fast an organism can assemble different memories. Out in the wild, the navigational problems a rat confronts are much more difficult--and potentially perilous--than anything in the laboratory. Ethologist are students of behavior in the wild. And ethologists Richard Lore and Kevin Flanders, undertook the frightening job digging up a rat-infested garbage dump in New Jersey to see how the beasts live out there. To Lore and Flander's surprise, they found that wild rats live in family groups, each with its own burrow. The dump wasn't honeycombed with one communal rat flop, the animals randomly infesting a labyrinth and eating, sleeping or mating wherever the opportunity presented itself. Now the wild rat is one vicious creature, as a child of the inner city can often testify first hand. A strange rat who ends up in the wrong hole isn't welcomed as an honored dinner guest but may very well become the piece de résistance. Thus when the rat ventures into the night and turns around to bring home a half-eaten pork chop, it by-god better know which burrow to choose out of hundreds in a multidimensional array. It would quickly succumb to its own social psychology if not for the superb navigational system resident in its hippocampus. The use to which a rat puts its hippocampus seems at least as complicated as ours. Appreciate, though, that while the qualitative features of the behaviors mediated by the homologous brains structures can differ greatly between them and us, the abstract attributes--the analogous logic-- can be quite similar. Let's remind ourselves of this from hologramic theory.

We can construct two continua that have identical numbers of dimensions yet produce different universes. How? The shape of a universe depends not only on how many dimensions it has, but on how they connect up and which part connects with what. Recall in the last chapter we envisaged adding a dimension by converting a figure 8 into a snowman.